"Attacking a candidate's religion is out of bounds, and our campaign will not engage in it, and we don't think others should either," campaign spokeswoman Lis Smith told Yahoo News by e-mail after Maher -- who gave $1 million to a so-called super political action committee backing Obama -- sent a message by Twitter saying:

"Why even listen to #MittRomney on foreign policy? His entire FP experience is 2 yrs trying to brow-beat Frenchmen into joining his cult" -- a reference to the former Massachusetts governor's 30 months in France in the late 1960s as a Mormon missionary.

Mormon missionaries, formally known as missionaries of the Church of Jesus Christ of Latter-day Saints, engage variously in proselytizing, church service and humanitarian aid, the church says.

The Romney campaign had no immediate comment on the Twitter message by Maher, a political satirist who has also insulted Democrats and defended Rush Limbaugh.

Maher, host of the HBO talk show "Real Time with Bill Maher" and a critic of religion in general, had no immediate response to the Obama campaign's disavowal of his Monday Twitter message.

Obama senior strategist David Axelrod told CNN's "State of the Union" Sunday Romney's faith was "not fair game" and said the campaign "absolutely" repudiated any effort to inject religion into the race.

Texas Gov. Rick Perry, a former Republican presidential hopeful, distanced himself in early October 2011 from prominent evangelical supporter the Rev. Robert Jeffress, pastor of the First Baptist Church in Dallas, who called the Mormon Church a cult.

It was "God's job," not Perry's, to judge people, a Perry spokesman said at the time, after saying Perry did "not believe Mormonism is a cult."

"Cult" was the top single word U.S. adults used in mid-November to describe the Mormon Church when asked for a Pew Forum on Religion & Public Life national poll.

The Mormon Church is the largest denomination in the Latter Day Saint movement, a Christian movement seeking what it considers to be a more pure, ancient form of Christianity. Adherents, referred to as Latter-day Saints, or informally as Mormons, view faith in Jesus and the atonement, or forgiveness of sin through Jesus' death by crucifixion, as the central tenet of their religion.

Under the doctrine of continuing revelation, Latter-day Saints believe Jesus leads the Mormon Church by revealing his will to its president, currently Thomas S. Monson.

The National Council of Churches classifies the Mormon Church as the fourth-largest Christian denomination in the United States.

David E. Campbell, a University of Notre Dame political science associate professor, said in the political journal Political Behavior that Romney's religion remained a "stained glass ceiling" that would be "a potential political stumbling block" for his presidential aspirations.

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